1. Field of the Invention
The present invention relates to a restoration method for a charging roller used for an electrophotographic apparatus. In the apparatus, a voltage-applied charging layer which forms the surface layer of the charging roller comes into contact with a member to be charged, by which the surface of this member is charged to a predetermined surface potential. The present invention further relates to a charging roller restored by the present invention. The present invention further relates to a process cartridge installed in a charging roller restored by the present invention.
2. Description of the Prior Art
As shown in FIG. 3, a charging roller is usually constituted of a conductive shaft 1, a conductive elastic cylinder 2, and a charging layer 3. The conductive elastic cylinder 2 is made of a conductive rubber, a conductive foamed material or the like, and is integrally formed on the conductive shaft 1. Further, the charging layer 3 is integrally provided on a peripheral surface of the conductive elastic cylinder 2. The charging layer 3 is provided as a thin layer by means of a dip-coating method, a spray coating method, and so forth. Alternatively, the peripheral surface of the conductive elastic cylinder 2 may be tightly covered with a seamless heat shrink charging tube.
Such a charging roller is used so as to come into contact with a member to be charged, which is a photosensitive drum for example. Due to the rubbing contact, a developing agent sometimes adheres to the surface of the charging roller. Moreover, the surface of the charging roller is abraded. In case the developing agent lightly adheres to the charging roller, it is possible to restore the charging roller by wiping the surface thereof with a cloth having absorbed therein an organic solvent such as an alcohol, a ketone and so forth. However, in case the developing agent adheres too strongly to be removed, the charging roller is incapable of being restored and is discarded. Also, in case the surface of the charging roller is scratched during handling and the surface thereof is deteriorated by electric discharge, the charging roller is discarded.
In order to overcome the above conventional problems, Japanese Patent Laid-Open Publication No. 8-171259 discloses a restoration method in which a used charging roller is covered with a seamless heat shrink tube-like charging layer. The Publication No. 8-171259 also discloses another restoration method in which a used charging roller is fitted into a seamless charging tube which forms a charging layer. FIG. 4 is a sectional view of the charging roller restored by the above-mentioned method. In FIG. 4, reference numeral 4 denotes a new charging layer tightly provided on a periphery of the charging roller. According to this method, the seamless charging tube which is to be the new charging layer is integrally attached to the used charging roller by a heat-shrinking method or a force fitting method. In the case of the heat-shrinking method, it is required to prepare a heat-shrinkable tube having an inner diameter larger than the outer diameter of the charging roller. Further, it is required to heat and shrink the heat-shrinkable tube after covering the charging roller. Conducting these steps is costly. In the case of the force fitting method, a seamless charging tube having an inner diameter smaller than the outer diameter of the charging roller is used. When the charging roller is forcibly inserted into the tube, the tube is likely to be damaged because the tube is physically weak. In view of this, practically, the charging roller is inserted into the tube in a state in which air is blown into the tube and the inner diameter thereof is expanded so as to be larger than the outer diameter of the charging roller. Such a process also incurs a considerable cost.
In the restoration method for the charging roller described in the Publication No. 8-171259, the new tube is overlapped on the outermost layer upon each restoration. In actuality, such restoration can be performed only once. The reason for this is that since the electric resistance of the initial charging roller is set so as to have best performance, when the surface of the charging roller is covered with the new tube, the electric resistance changes to shift from the best performance. In practice, this shift from the best performance is imperceptible and hardly causes any problems. However, when a surface of the new tube is further covered with another tube, the shift from the best performance increases. Moreover, the diameter of the restored charging roller is not constant over the entire surface of the charging roller, since the surface of the used charging roller is neither clean nor smooth. Under these conditions, in some cases print quality obtained by using such a charging roller is not acceptable. For example, when a halftone pattern is printed using the charging roller, unevenness arises in the halftone pattern. Also, when printing is conducted in an environment of low humidity and low temperature, a considerable amount of fog may appear on the background of the print.
As to the restoration method for the charging roller described in the Publication No. 8-171259, it has been further found that the following problem arises. When the surface of the charging roller has an uneven portion having a size of about 50 xcexcm or more (depth or height of about 50 xcexcm or more, and width (or shorter diameter) of about 50 xcexcm or more, a print having an uneven portion can be obtained. The reason for this is explained referring to FIG. 5 in which reference numeral 4 denotes a new charging layer provided by a conventional restoration process. The charging layer 4 is formed in such a manner that a heat-shrinkable tube loosely covers the surface of the charging roller to be restored, and then heated to shrink the tube and tightly covers the surface of the charging roller to be restored. At this time, if there is an uneven portion 5 on the surface of the charging roller, a concave portion 6 having a similar shape to the uneven portion 5 is caused on the surface of the restored charging roller, because the heat-shrinkable tube shrinks along the surface of the uneven portion. In FIG. 5, depth of the uneven portion 5 reaches only to the charging layer 3. The uneven portion 5, however, sometimes reaches to the conductive cylinder 2. It was confirmed that when the concave portion 6 was formed, charging was not performed at this portion or charging was not uniformly performed.
In the above, is described the case of the uneven portion having a concave shape. A similar phenomenon also occurs when something adheres to the surface of the charging roller to form a convex shape.
When there is a convex portion on the surface of the restored charging roller, the convex portion always comes into contact with the photosensitive drum strongly. Due to this, the contact portion is locally deteriorated, which shortens the lifetime of the charging roller. It was confirmed that the lifetime of the photosensitive drum was also shortened. Even if the size of the convex portion is about 50 xcexcm or less and uneven charging is not caused at the beginning, the progressive deterioration causes uneven charging at the convex portion to cause the lifetime to be shortened. When a concave portion is formed on the surface the above-described phenomenon also occurs, since the edge thereof strongly comes into contact with the photosensitive drum.
As stated above, in the conventional restoration method for the charging roller, there are problems in conducting the restoration repeatedly, in conducting it at a low cost, and in obtaining a reproduced charging roller of a high quality.
In view of the foregoing, it is a primary object of the present invention to provide a restoration method for a charging roller, by which restoration can be performed plural times.
It is a second object of the present invention to provide a restoration method for a charging roller in which restoration can be performed even if an unevenness of about 50 m or more exists on the surface of the charging roller to be restored.
It is a third object of the present invention to provide a restoration method for a charging roller in which the lifetime of the charging roller is not shortened even if there is an unevenness on the surface of the charging roller prior to restoration.
It is a fourth object of the present invention to provide a restoration method for a charging roller which is low in cost.
It is a fifth object of the present invention to provide a charging roller restored by the method of the present invention.
It is a sixth object of the present invention to provide a process cartridge installed in a charging roller restored by the method of the present invention.
Other objects will be apparent from the following descriptions.
The objects of the present invention can be achieved by restoration method comprising a step of loosely encasing a used charging roller in a seamless charging tube.
The charging roller restored according to the present invention is constituted of a conductive shaft, a conductive elastic cylinder, and at least one charging layer. The conductive elastic cylinder is integrally formed on the peripheral surface of the conductive shaft. Further, the charging layer is integrally provided on the peripheral surface of the conductive elastic cylinder. According to the present invention a used charging roller is restored by loosely encasing the charging roller in a seamless charging tube.
In a preferred embodiment of the present invention, the charging roller is loosely encased in the seamless charging tube for restoration after a cleaning process has been performed on the surface of the charging roller to which dust has adhered. As to the cleaning process, there are several methods, for example, a method wherein air blowing or an organic solvent is used, and an abrasion method.
When the charging roller restored by the present invention is used for a long time, the seamless charging tube is gradually deteriorated. Such a charging roller may be restored again according to the present invention, i.e., by replacing the deteriorated seamless charging tube with a new one. According to the present invention, the charging roller may be similarly restored repeatedly.
In another embodiment of the present invention, it is possible to restore a charging roller which has been restored by integrally and tightly covering it with a new charging layer by a method as stated, for example, in the Publication No. 8-171259. In other words, according to the present invention it is possible to restore a charging roller having two charging layers.
In the other embodiment of the present invention, the deteriorated charging layer of a charging roller is peeled off to expose the conductive elastic cylinder. This exposed elastic cylinder is loosely encased in the seamless charging tube.
According to the present invention, the charging roller may be restored repeatedly. Further, restoration may be performed without using an organic solvent. Thus, there are advantages with respect to economical use, easy restoration, and the environment.